1. Field of the Invention
This invention relates to a multiple-pane glazing unit and in particular to a glazing unit incorporating a peripheral insulating spacing-and-sealing assembly.
2. Description of the Prior Art
Conventional multiple-pane glazing units consist of two or more parallel sheets of glass which are typically spaced apart from each other using a peripheral spacing-and-sealing assembly which conventionally consists of a inner hollow metal spacer filled with desiccant-bead material and an outer hermetic-seal made from sealant material which adheres to the glazing sheets and the back face of the metal spacer. To reduce radiation heat loss, the glazing units can incorporate a low-emissivity coating which is applied to one of the glazing sheets and to further reduce conductive heat loss from the glazing, the cavity between the glazing sheets can also be filled with a low-conductive gas such as argon. Conductive heat loss through the spacing-and-sealing assembly can also be reduced by replacing the conductive metal spacer with an insulating spacer.
As disclosed in U.S. Pat. No. 4,831,799 issued to Glover et al., one advantage of substituting an insulating spacer is that the cold-weather problem of edge-of-glass condensation is diminished. However, experience has shown that although the substitution of an insulating spacer substantially reduces conductive heat loss through the perimeter edge seal, condensation at the bottom edge-of-glass area can still occur particularly if there is extreme cold weather and high interior humidity levels. These cold bottom-edge temperatures are primarily caused by surface convective flow of the air or gas fill within the high thermal-performance, double-glazed units.
In the past, various assemblies have been incorporated within the double-glazed unit and although typically these assemblies were added for mainly aesthetic reasons, these assemblies will also tend to interfere with surface convective flow within the unit. Listed below are examples from the prior art.
U.S. Pat. No. 49,167 issued to Stetson, describes the use of wood studs which are incorporated in the sealed unit to prevent the center parts of the glazing sheets from coming in contact with each other.
U.S. Pat. No. 2,132,217 issued to Neuendorf, describes a muntin-bar grid incorporated in a sealed unit in order to give the appearance of divided lights and this muntin-bar grid creates a series of small dead-air spaces and as a result, convective flow within the sealed unit is reduced to some degree.
U.S. Pat. No. 2,915,793 issued to Berg, describes a sealed glazing unit incorporating a venetian window-blind assembly suspended between the glazing sheets and this blind assembly provides privacy and also helps control light transmission. The venetian-blind assembly consists of moveable, closely-spaced, horizontal slats which create a series of small dead air spaces and as a result, convective flow within the sealed unit is reduced to some degree.
U.S. Pat. No. 4,207,507 issued to Hart, describes a solar-collector panel with a series of horizontal strips of transparent-film material suspended between the glazing sheets. These flat parallel strips which are spaced closely together, are specifically designed to reduce convective heat loss between the solar collector absorber and the exterior glazing. Compared to vertically-installed windows, convective heat loss for solar collectors is a more significant problem because these collectors are operated at higher temperatures and are typically installed at an inclined slope or angle. Hart also describes a window assembly of similar construction to the solar-collector panel except that the solar absorber and collector housing are replaced by a second transparent glazing panel. Because the inner and outer glazing layers are spaced widely apart, a series of circular convective-flow cells are set up between the two glazing sheets and the horizontal strips are designed to reduce this air or gas circulation between the glazing sheets. However for a conventional sealed unit, the glazing sheets are spaced closer together and as a result of the reduced cavity width, convective circulation between the glazing layers is substantially reduced. Further it should be noted that as with the other previously-described additions to the air-space, the horizontal strips do not specifically address the problem of convective flow at the bottom edge of the cavity.